This disclosure is related to the field of measuring instruments and/or wellbore intervention instruments for determining petrophysical properties of subsurface formations traversed by a wellbore and/or performing intervention operations in wellbores. More specifically, the disclosure relates to improving accuracy of measurement of axial position (depth) of such instruments in a wellbore.
U.S. Patent Application Publication No. 2016/0032711 describes an apparatus for measuring movement of a wellbore measuring instrument or intervention apparatus along the interior of a wellbore. The instrument or apparatus may be moved along the wellbore using a winch and cable, coiled tubing, drill pipe, jointed tubing, tractor or any other known conveyance. A record is made of the movement of the conveyance proximate the earth's surface. Because the conveyance may be of considerable length, correspondence between movement of the conveyance at the surface and the wellbore instrument or apparatus may be inaccurate. This is particularly the case where the instrument or apparatus undergoes “stick-slip” motion, wherein the instrument or apparatus momentarily is stopped by one or more types of obstruction in the wellbore. While the instrument or apparatus is stationary during stick times, the value of the surface measurement of the conveyance continues to change. This process may continue until the instrument or apparatus is freed from being stuck. At such time the instrument or apparatus may accelerate until excess tension or compression in the conveyance is relieved. The '711 publication describes measuring wheels placed in contact with the wall of the wellbore and accelerometers that in combination make measurements of movement of the instrument or apparatus proximate thereto so that effects of elongation and/or shortening of the conveyance not directly resulting from operation of the conveyance at the surface may be attenuated and a more accurate determination of instrument or apparatus movement may be made.
According to the disclosure of the '711 publication an embodiment of an apparatus for measuring at least one of downhole position and velocity includes a body. A roller is connected with the body, and a plurality of sensors is connected with the body. The plurality of sensors acquires roller data and wellbore data. The roller data and wellbore data are used to determine the velocity, position, or both of the apparatus. The apparatus also includes an electronic module. The electronic module is in communication with the set of sensors. An example method of monitoring an apparatus in a wellbore includes acquiring roller data related to the number of revolutions of a roller connected to a body of an apparatus. The example method also includes acquiring wellbore data related to wellbore properties, transmitting the roller data and wellbore data to a processor. The example method further includes determining at least one of velocity of the apparatus and position of the apparatus in the wellbore. An example method of monitoring an apparatus in a wellbore includes measuring the number of revolutions of a roller connected with an apparatus, and acquiring wellbore data related to formation properties. The method also includes determining the velocity of the apparatus using the wellbore data and the measured number of revolutions.
The foregoing methods and apparatus according to the '711 publication assume accurate correspondence between motion of the instrument and rotation of the wheel(s). Wellbore and/or formation conditions may make such assumption inaccurate.